The enqueuer should never encouter the "From " separator in its headers, as

The enqueuer should never encouter the "From " separator in its headers, as
it is added by the mda. If it sees one, it means that the enqueuer was used
as the mda and it needs to strip it otherwise the message will end with two
delimiters later down the road. Same applies to "Return-Path".

bug experienced by James Turner, confirmed by Giovanni.
fix suggested by Todd Miller, diff ok eric@